Core-shell type anode active material for lithium secondary battery, method for preparing the same and lithium secondary battery comprising the same

ABSTRACT

The present invention relates to a core-shell type anode active material for a lithium secondary battery, a method of preparing the same, and a lithium secondary battery comprising the same. The anode active material for a lithium secondary battery according to the present invention comprises a carbon based material core portion; and a shell portion formed outside of the carbon based material core portion by coating the carbon based material core portion with a spinel-type lithium titanium oxide. The anode active material for a lithium secondary battery according to the present invention has the metal oxide shell portion, and thus has the improved conductivity, a high output density, and consequently excellent electrical characteristics.

TECHNICAL FIELD

The present invention relates to a core-shell anode active material fora lithium secondary battery, a method for preparing the same, and alithium secondary battery comprising the same. In particular, thepresent invention relates to an anode active material, which can improveelectrical characteristics and safety of a lithium ion secondary batteryor lithium ion polymer battery, and a method for preparing the same.

BACKGROUND ART

With rapid development of electronics, communications and computerindustries, portable electronic communication equipments such ascamcorders, mobile phones or notebook computers develop remarkably.Accordingly, the demand for a lithium secondary battery as a powersource for driving the portable electronic communication equipments isincreasing day by day. In particular, in application of electricvehicles, uninterruptible power supplies, motor tools or artificialsatellites, research and development of the lithium secondary battery asan environmentally friendly power source is lively made inside andoutside of the country including Japan, Europe and U.S.A.

Currently, an anode active material for a lithium secondary batteryincludes a crystalline carbon such as a natural graphite or anartificial graphite, and an amorphous carbon such as a non-graphitizablecarbon or a graphitizable carbon.

The natural graphite has advantages of low price, a flat discharge curveat a negative potential and excellent initial discharge capacity.However, charge/discharge efficiency and charge/discharge capacityreduce remarkably while charge and discharge cycles are repeated.

A mesophase graphite has a spherical particle shape and allows a highdensity filling, and thus is capable of improving an energy density pervolume of a battery and exhibits excellence in forming an electrodeplate. However, the mesophase graphite has a disadvantage of a lowreversible capacity.

The non-graphitizable carbon has advantages of excellent safety and alarge capacity. However, the non-graphitizable carbon has smaller sizethan a graphitizable carbon, and has a micropore, consequently lowdensity, and after a pulverizing process, has irregular particle shapeand particle size, and therefore, the non-graphitizable carbon isdifficult to be applied to a battery widely.

And, to meet the demand for safety and a large capacity, a recentattention is given to a lithium titanium oxide. The lithium titaniumoxide is an anode active material having a spinel-type stable structure,and thus is evaluated as one of materials capable of improving safety.In the case that the lithium titanium oxide is used as an anode activematerial, the lithium titanium oxide shows flatness of a potentialcurve, excellent charge and discharge cycle, improved high ratecharacteristics and power characteristics, and excellent durability.However, in the case that the lithium titanium oxide is used singularly,battery characteristics are reduced due to a low average voltage.

Therefore, various methods are suggested to solve the problems of theconventional anode active material. So far, however, there is no reportof such an anode active material evaluated as it has excellentelectrical characteristics and safety of a lithium secondary battery.

For example, Korean Patent Registration No. 10-066822 discloses a methodfor coating the surface of a conventional carbon with a metal ormetalloid for a large capacity and a high efficiency of a battery.

Korean Patent Registration No. 10-0433822 discloses a method for coatingthe surface of a carbon active material with a metal or metal oxide toimprove conductivity, high rate charge and discharge characteristics andcycle life.

Korean Laid-open Patent Publication No. 10-2007-0078536 discloses amethod for coating a natural graphite with a low crystallinity carbonmaterial.

Korean Laid-open Patent Publication No. 10-2006-0106761 discloses amethod for adding graphite or carbon black to a lithium titanium oxideso as to prevent overcharge.

However, the methods suggested in the above-mentioned prior arts areevaluated as not sufficiently exhibiting effects of maintainingelectrical characteristics well and improving safety of a lithiumsecondary battery.

Therefore, it requires to suggest an anode active material capable ofmaintaining excellent battery characteristics and exhibiting anexcellent safety and a method for preparing the cathode active materialwith excellent reproducibility and productivity.

DISCLOSURE OF INVENTION Technical Problem

An object of the present invention is to provide an anode activematerial for a lithium secondary battery, which can improve safetywithout deteriorating basic battery characteristics of the lithiumsecondary battery, and a method for preparing the anode active materialwith excellent reproducibility and productivity.

Technical Solution

In order to achieve the above-mentioned object, an anode active materialfor a lithium secondary battery according to the present inventioncomprises a carbon based material core portion, and a shell portionformed outside of the carbon based material core portion by coating thecarbon based material core portion with a spinel-type lithium titaniumoxide. The anode active material for a lithium secondary batteryaccording the present invention comprises the metal oxide shell portionto improve conductivity and high output density, thereby resulting inexcellent electrical characteristics. And, a lithium secondary batteryusing the above-mentioned anode active material for a lithium secondarybattery according to the present invention can ensure safetysufficiently.

And, a method for preparing an anode active material for a lithiumsecondary battery according to the present invention comprises (S1)preparing a carbon based material for forming a core portion; and (S2)coating the core portion with a spinel-type lithium titanium oxide toform a shell portion outside of the core portion.

The method for preparing an anode active material may further compriseheating the resultant product of the step (S2).

The above-mentioned anode active material for a lithium secondarybattery may be used to manufacture an anode of a lithium secondarybattery and a lithium secondary battery comprising the anode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating particle size distribution before coating(a) and after coating (b) of an anode active material prepared inExample 1.

FIG. 2 shows SEM (Scanning Electron Microscope) photographs of the anodeactive material (a) prepared in Example 1 and an anode active material(b) prepared in Comparative example 1.

FIG. 3 shows SEM photographs of cross-sectional mapping of particles ofthe core-shell anode active material prepared in Example 1.

FIG. 4 is a graph illustrating discharge characteristics according tocurrent density of a lithium secondary battery (a) using the anodeactive material prepared in Example 1 and a lithium secondary battery(b) using the anode active material prepared in Comparative example 1.

FIG. 5 is a graph illustrating discharge characteristics according totemperature of the lithium secondary battery (a) using the anode activematerial prepared in Example 1 and the lithium secondary battery (b)using the anode active material prepared in Comparative example 1.

FIG. 6 is a graph illustrating changes in battery behavior and surfacetemperature after an overcharge test at 30V of the lithium secondarybattery (a) using the anode active material prepared in Example 1 andthe lithium secondary battery (b) using the anode active materialprepared in Comparative example 1.

FIG. 7 is a graph illustrating changes in battery behavior and surfacetemperature after a nail penetration test of the lithium secondarybattery using the anode active material prepared in Example 1.

MODE FOR THE INVENTION

Hereinafter, a cathode active material for lithium secondary batteriesof the present invention will be described in detail according to itspreparation method. Prior to the description, it should be understoodthat the terms used in the specification and the appended claims shouldnot be construed as limited to general and dictionary meanings, butinterpreted based on the meanings and concepts corresponding totechnical aspects of the present invention on the basis of the principlethat the inventor is allowed to define terms appropriately for the bestexplanation. Therefore, the description proposed herein is just apreferable example for the purpose of illustrations only, not intendedto limit the scope of the invention, so it should be understood thatother equivalents and modifications could be made thereto withoutdeparting from the spirit and scope of the invention.

First, a carbon based material for forming a core portion is prepared(S1).

The carbon based material usable in the present invention is not limitedto a specific material if it is a carbon based material used as an anodeactive material for a lithium secondary battery in the prior art. Forexample, the carbon based material includes a low crystallinity carbonand a high crystallinity carbon. Typically, the low crystallinity carbonincludes a soft carbon and a hard carbon, and the high crystallinitycarbon includes a high temperature plasticity carbon such as a naturalgraphite, Kish graphite, a pyrolytic carbon, a mesophase pitch basedcarbon fiber, meso-carbon microbeads, mesophase pitches, and petroleumor coal tar pitch derived cokes.

Next, the core portion is mated with a spinel-type lithium titaniumoxide to form a shell portion outside the core portion (S2).

The anode active material of the present invention is prepared bycoating the carbon based material core portion with the spinel-typelithium titanium oxide, thereby improving the battery performance. Forexample, in the case of a natural graphite, charge/discharge efficiencyand charge/discharge capacity reduce remarkably while charge anddischarge cycles are repeated, which is resulted from a decompositionreaction of an electrolyte liquid occurring at an edge portion of thenatural graphite of high crystallinity. However, in the case that thenatural graphite is mated with the shell portion according to thepresent invention, the reaction between the edge portion and theelectrolyte liquid is prevented to solve the above-mentioned problems.And, in the case of a low crystallinity carbon, suppressing effects ofreactivity with an electrolyte and moisture sensitivity are increasedthrough surface mating according to the present invention, therebyimproving the battery performance.

The shell portion of the present invention is described in detail asfollows.

In the anode active material of the present invention, charging isperformed on the spinel-type lithium titanium oxide (Li₄Ti₅O₁₂) for theshell portion in the proximity of 1.0 to 1.2V based on a lithium metalearlier than the carbon based material for the core portion, so that afilm having good ion conductivity in the above-mentioned range is formedon the surface of an anode. And, an activated lithium titanium oxidelayer reduces resistance of the surface of the anode. As a result, theanode active material of the present invention can have excellentelectrical characteristics.

And, the film suppresses a reaction between the carbon based materialcorresponding to the core portion and a non-aqueous electrolyte liquid,and thus it prevents phenomena that the non-aqueous electrolyte liquidis decomposed or a stricture of the anode is destroyed. And, the lithiumtitanium oxide of the shell portion and the film surround the carbonbased material core portion, so that a contact between the core portionand the electrolyte liquid is restricted. Accordingly, a phenomenon thatlithium is educed on the surface of the anode active material issuppressed to reduce an amount of heat involved in the reaction with theelectrolyte liquid. Therefore, the anode active material of the presentinvention can provide excellent battery performance and safety.

A content of the spinel-type lithium titanium oxide for the shellportion may be selected properly according to purpose of use, kind or amanufacturing environment of a lithium secondary battery. For example, aweight ratio of the carbon based material core portion to thespinel-type lithium titanium oxide shell portion is adjusted such thatthe carbon based material:the spinel-type lithium titaniumoxide=1:0.0055˜0.05. The above-mentioned range can have an intentionaleffect of the present invention because a redundant lithium titaniumoxide does not leave behind and the entire surface of the carbon basedmaterial is sufficiently coated.

An average particle size of the spinel-type lithium titanium oxide forthe shell portion may vary depending on purpose of use or manufacturingenvironment, for example 30 to 800 nm. The above-mentioned range ispreferable because agglomeration of particles is minimized and a coatingprocess is performed effectively.

A method for coating the carbon based material core portion with thespinel-type lithium titanium oxide may use a typical coating processused in the prior art without limitation, and select a coating processproperly according to necessity. For example, the typical coatingprocess includes a dry coating process and a wet coating process.

The wet coating process allows uniform dispersion of coating materials.For a specific example, the wet coating process is performed as follows:a dispersion liquid or suspension liquid, in which coating materials aredispersed, or a solution in which coating materials are dissolved issprayed onto or impregnated into the anode active material and dried.

And, the dry coating process coats the surface of a core portion withcoating materials for a shell portion in a mechanical manner. A shearforce, a collision force or a compression force is applied according tonecessity, thereby allowing from simple mixing to coating. Inparticular, in the present invention, sphericity and disintegrationoccur to the carbon based material corresponding to the core portion bythe nano metal oxide corresponding to the shell portion, therebyimproving powder characteristics.

After the shell portion is coated as mentioned above, heating may befurther performed according to necessity. The heating increases anadhesive strength between the carbon based material and the lithiumtitanium oxide, and removes impurities.

The heating conditions may be selected properly according to amanufacturing environment such as kind of the carbon based material forthe core portion, for example the heating may be performed at 400 to450° C. for 1 to 4 hours, however the present invention is not limitedin this regard. The above-mentioned heating temperature is preferablebecause the density of the shell portion is excellent, a defect incrystal structure of the core portion can be corrected sufficiently andthe structure of the core portion can be maintained stably. In theabove-mentioned heating time, an effect of the heating can be obtainedsufficiently, and in the case that the heating time exceeds 4 hours, anadditional effect by the increased heating time can not be expected.

Through the above-mentioned method, an anode active material of thepresent invention can be obtained, and an anode of a lithium secondarybattery and a lithium secondary battery can be manufactured using thesame. In the manufacture of the anode of a lithium secondary battery andthe lithium secondary battery using the anode active material of thepresent invention, a typical method used in the prior art can be appliedwithout limitation.

A method for manufacturing a lithium secondary battery is described asfollows.

First, an electrode active material composition including an electrodeactive material, a binder, a conductive material and a solvent is coatedon a current collector to form an electrode active material layer. Atthis time, the electrode active material layer is formed such that theelectrode active material composition is directly coated on the currentcollector, or such that the electrode active material composition iscoated on a separate support and dried to form a film, and the film isseparated from the support and laminated onto the current collector.Here, the support is not limited to a specific one if it is capable ofsupporting the electrode active material layer, for example a Mylar filmor a polyethyleneterephthalate (PET) film.

The cathode electrode active material, binder, conductive material andsolvent may be all typical ones used to manufacture a lithium secondarybattery in the prior art. For a specific example, an electrode activematerial for a cathode may be a lithium-containing metal oxide such asLiCoO₂, LiNiO₂ and LiMn₂O₄ or a lithium-containing metal oxide obtainedby adding Co, Ni or Mn to the above-mentioned lithium-containing metaloxide, such as LiNi_(1-x)Co_(x)O₂, and may be sulfide, selenide orhalide other than the above-mentioned oxides.

The binder may be polyvinylidenefluoride-hexafluoropropylene copolymer(PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile,polymethylmethacrylate, or mixtures thereof. Typically, the conductivematerial may be carbon black or acetylene black, and the solvent may beacetone or N-methylpyrrolidone.

An electrode is formed as mentioned above, and a separator is interposedbetween a cathode electrode plate and an anode electrode plate, and thusan electrode assembly is manufactured. Subsequently, the manufacturedelectrode assembly is put into a case and an electrolyte liquid for alithium secondary battery is added, so that a lithium secondary batteryof the present invention is completed.

Hereinafter, the preferred embodiments of the present invention aredescribed in detail with reference to the accompanying drawings.However, it should be understood that the detailed description andspecific examples, while indicating preferred embodiments of theinvention, are given by way of illustration only, since various changesand modifications within the spirit and scope of the invention willbecome apparent to those skilled in the art from this detaileddescription.

Example 1

Preparing of Core-Shell Type Anode Active Material

Meso-carbon microbeads (MCMB) (Osaka Gas Co., Ltd.) were prepared as acarbon based material for a core portion, and a spinel-type lithiumtitanium oxide having a particle size distribution of 30 to 500 nm wasprepared as a material for a shell portion. 1,000 g of the prepared MCMBwas mixed with 20 g of the lithium titanium oxide, and the mixture wastreated in a dry coating system (Hosokawa Micron Corp., Japan, NOB-130)with a speed of rotation of 2500 rpm for 3 minutes. Subsequently, theresultant was heated at 450° C. under an oxygen atmosphere for 4 hourswith a temperature increase rate of 2° C./min to prepare a core-shelltype anode active material.

Manufacturing of Anode and Lithium Secondary Battery

The prepared anode active material, a conductive carbon for providingconductivity, and PVdF (polyvinylidenefluoride) as a binder were mixedwith a mixing ratio of 85/8/7, and a proper amount of NMP(N-methylpyrrolidone) was added to obtain a slurry having a properviscosity. The slurry was coated on a copper foil, dried and compressedto obtain an anode of a lithium secondary battery.

A lithium metal oxide composite, LiNi_((1-x-y))Mn_(x)Co_(y)O₂ was usedas a cathode, a separator was interposed between the above-mentionedanode and cathode, and an aluminum outer member was applied tomanufacture a lithium secondary battery. The battery had a size of 4.5mm thickness×64 mm width×95 mm length, and a design capacity of 2000mAh.

Example 2

An anode active material, an electrode and a lithium secondary batterywere manufactured by the same method as that of the Example 1, exceptthat 10 g of a lithium titanium oxide was used and heating was notperformed.

Example 3

An anode active material, an electrode and a lithium secondary batterywere manufactured by the same method as that of the Example 1, exceptthat heating was not performed.

Example 4

An anode active material, an electrode and a lithium secondary batterywere manufactured by the same method as that of the Example 1, exceptthat 30 g of a lithium titanium oxide was used and heating was notperformed.

Example 5

An anode active material, an electrode and a lithium secondary batterywere manufactured by the same method as that of the Example 1, exceptthat 50 g of a lithium titanium oxide was used and heating was notperformed.

Comparative Example 1

An electrode and a lithium secondary battery were manufactured by thesame method as that of the Example 1, except that only MCMB was usedinstead of the core-shell type anode active material.

Comparative Example 2

An electrode and a lithium secondary battery were manufactured by thesame method as that of the Example 1, except that a mixture of MCMB anda lithium titanium oxide mixed with a weight ratio of 90:10 was used asan anode active material instead of the core-shell type anode activematerial.

Characteristics Evaluation

1. Powder Characteristics

The average particle size, D₁₀, D₅₀ and D₉₀ before and after coating ofanode active materials prepared in the examples was measured by a laserdiffraction technology while particles were dispersed using ultrasonicwaves. A particle size analysis system (Malvern Instruments, Mastersizer2000E) was used to measure the average particle size. FIG. 1 showsmeasurement results of an anode active material prepared in the Example1, and as a specific data, an average particle size before coating is asfollows D₁₀=15.380 μm, D₅₀=23.519 μm, and D₉₀=36.396 μm, and an averageparticle size after coating is as follows: D₁₀=15.291 μm, D₅₀=21.795 μm,and D₉₀=31.054 μm.

And, 500 times of strokes were performed using 100 ml mass cylinder tomeasure a tap density, and changes in volume between before coating andafter coating were measured.

As a result of the measurement, the average particle size and tapdensity hardly changed according to coating content, and after coating,the average particle size was decreased by 8 to 9%, and the tap densitywas increased by 1 to 2%.

2. Coating Characteristics

To check the surface characteristics of the Example 1 and Comparativeexample 1, results measured using SEM (Scanning Electron Microscope) areshown in FIG. 2. And, mapping of the core-shell type cathode activematerial obtained in the Example 1 is shown in FIG. 3. As shown in FIGS.2 and 3, the carbon based material of the present invention is coateduniformly with a lithium titanium oxide.

3. Electrochemical Characteristics

The batteries manufactured in the examples and the comparative exampleswere initially charged using a charge/discharge cycle system onconditions of CC-CV (constant current-constant voltage) of a chargevoltage of 4.2 V and a current density of 400 mAh at 25° C., and after aresting stage of 10 minutes, were discharged with a discharge capacityof 1000 mAh until the voltage is 2.7 V, and electrical characteristicsand safety were evaluated.

And, to evaluate an extent of improvement of conductivity, dischargecharacteristics and low temperature discharge characteristics accordingto current density were measured. The discharge characteristicsaccording to current density were measured by charging on conditions ofCC-CV of a current density of 2000 mAh and a charge voltage of 4.2 V at25° C., and after a resting stage of 10 minutes, discharging with adischarge current of 0.5 C to 20.0 C until the voltage is 2.7 V. And,the discharge characteristics according to current density shows as aratio of a discharge capacity at a current density of 20 C to adischarge capacity at a current density of 0.5 C (1000 mA) as a standardcapacity with using high rate characteristics before and after coatingare shown in the following Table 2. FIG. 4 is a graph illustratingdischarge characteristics (a) according to current density of theExample 1 and discharge characteristics (b) according to current densityof the Comparative example 1. Further, a low temperature dischargecharacteristics test was made at −10° C. and −20° C. with a currentdensity of 1 C in the voltage range of 2.5 V to 4.2 V with a dischargecapacity of 1 C at 25° C. as a standard capacity. The following Table 2shows the low temperature discharge characteristics, and FIG. 5 showslow temperature discharge characteristics of the Example 1 and theComparative example 1.

As shown in the following Table 1, as the coating content of lithiumtitanium oxide increases, initial charge/discharge efficiency andspecific rapacity are reduced, however, it is found through the Table 2and FIGS. 4 and 5 that conductivity was improved due to high ratedischarge characteristics and low temperature discharge characteristics.

And, an overcharge test and a nail penetration test were made on theanode active materials prepared in the Example 1 and the Comparativeexample 1. The overcharge test was made with a current density of 2000mA at 18 V, 24 V and 30 V to measure changes in shape and surfacetemperature of a battery after overcharge, and measurement results areshown in the following Table 3. FIG. 6 shows changes in battery behaviorand surface temperature after an overcharge test at 30V (Example 1: a,Comparative example 1: b). After evaluation of the nail penetrationtest, the surface temperature of a battery is shown in Table 3, and FIG.7 shows changes in battery behavior and surface temperature of theExample 1.

TABLE 1 Coating 1st 1st 1st Specific content charge discharge efficiencycapacity Classification (weight %) (mAh) (mAh) (%) (mAh/g) Example 12.0, heating 2440 2100 86.5 145.0 Example 2 1.0 2400 2100 87.7 147.0Example 3 2.0 2450 2120 86.5 145.0 Example 4 2.9 2410 2010 83.6 140.0Example 5 4.8 2450 1970 80.3 134.6 Comparative 0.0 2400 2130 88.5 152.0example 1 Comparative 10, mixing 2370 1880 79.5 133.3 example 2

TABLE 2 20 C Low temperature discharge discharge characteristics Coatingcharacter- @ −10° C. @ −20° C. content istics (@ (@ 25° C., (@ 25° C.,Classification (weight %) 0.5 C, %) %) %) Example 1 2.0, heating 96.693.4 86.0 Example 2 1.0 88.6 87.9 80.2 Example 3 2.0 93.7 93.0 82.8Example 4 2.9 91.5 90.9 79.6 Example 5 4.8 85.3 88.3 70.3 Comparative0.0 84.9 85.6 77.8 example 1 Comparative 10, mixing 80.4 79.6 68.3example 1

TABLE 3 Battery behavior, Coating maximum battery Nail content surfacetemperature (° C.) penetration Classification (weight %) 18 V 24 V 30 Vtest Example 1 2.0, heating A, 60 A, 72 A, 83 A, 65 Example 2 1.0 A, 85C, 180 x B, 103 Example 3 2.0 A, 65 A, 74 A, 86 A, 68 Example 4 2.9 A,56 A, 70 A, 80 A, 63 Example 5 4.8 A, 52 A, 64 A, 77 A, 63 Comparative0.0 D, 270 x x D, 310 example 1 Comparative 10, mixing C, 180 x x C, 200example 2 A: no change, B: smoke generation, C: fire, D: explosion

The above Tables show that the Examples 1 to 5 have a little lowerinitial charge/discharge efficiency and specific capacity than theComparative example 1, and this is because the surface of MCMB is coatedwith a nano-sized lithium titanium oxide, consequently an irreversiblecapacity occurs at the other potential area, and as a result, theExamples 1 to 5 exhibit a little low specific capacity. However, this isnot an important factor to battery characteristics. On the contrary, theComparative example 1 shows higher initial charge/discharge efficiencyand specific capacity, but shows very weak characteristics in theevaluation about conductivity and safety.

However, the examples prevent a side reaction with an electrolyte liquidand reduces resistance of the surface of an active material by anactivated shell coating layer, and thus show considerable improvement ofhigh rate characteristics and low temperature discharge characteristics.In particular, through heating after coating, the Example 1 increases anadhesive strength between a carbon based material and a lithium titaniumoxide and has an impurity removing effect, and thus is more effective inimprovement of performance.

Meanwhile, in the case of an anode active material of the Comparativeexample 2, obtained by simply mixing a carbon based material and alithium titanium oxide, because the carbon based material and thelithium titanium oxide are operated at different voltage ranges,performance of a battery is reduced and safety does not take effect.

INDUSTRIAL APPLICABILITY

An anode active material for a lithium secondary battery according tothe present invention comprises a carbon based material core portion anda spinel-type lithium titanium oxide shell portion, and thus, a lithiumsecondary battery using the same exhibits excellent electricalcharacteristics and safety. And, a method for preparing the anode activematerial for a lithium secondary battery according to the presentinvention has excellent reproducibility and productivity in preparingthe core-shell type anode active material of the present invention.Therefore, the present invention is useful in an industrial applicationof a lithium secondary battery.

1. An anode active material for a lithium secondary battery, comprising:a carbon based material core portion; and a shell portion formed outsideof the carbon based material core portion by coating the carbon basedmaterial core portion with a spinel-type lithium titanium oxide.
 2. Theanode active material for a lithium secondary battery according to claim1, wherein the carbon based material for forming the core portion is anyone selected from the group consisting of a soft carbon, a hard carbon,a natural graphite, Kish graphite, a pyrolytic carbon, a mesophase pitchbased carbon fiber, meso-carbon microbeads, mesophase pitches, andpetroleum or coal tar pitch derived cokes, or mixtures thereof.
 3. Theanode active material for a lithium secondary battery wording to claim1, wherein the spinel-type lithium titanium oxide has an averageparticle size of 30 to 800 nm.
 4. The anode wave material for a lithiumsecondary battery wording to claim 1, wherein a weight ratio of thecarbon based material core portion to the spinel-type lithium titaniumoxide shell portion is adjusted such that the carbon based material: thespinel-type lithium titanium oxide=1:0.0055˜0.05.
 5. A method forpreparing an anode active material for a lithium secondary battery,comprising: (S1) preparing a carbon based material for forming a coreportion; and (S2) coating the core portion with a spinel-type lithiumtitanium oxide to form a shell portion outside of the core portion. 6.The method for preparing an anode active material for a lithiumsecondary battery according to claim 5, wherein, in the step (S2), thecoating process is a dry coating process.
 7. The method for preparing ananode active material for a lithium secondary battery according to claim5, further comprising: heating the resultant product of the step (S2).8. The method for preparing an anode active material for a lithiumsecondary battery according to claim 7, wherein the heating is performedat 450 to 500° C. for 1 to 4 hours.
 9. An anode of a lithium secondarybattery, comprising: an anode collector; and an anode active materiallayer including an anode active material, a binder and a conductivematerial, and formed on at least one surface of a anode collector,wherein the anode active material is defined in any one of claims 1 to4.
 10. A lithium secondary battery comprising: a cathode; an anode; anda separator interposed between the cathode and the anode, wherein theanode is defined in claim 9.